This invention relates to multi-speed power transmissions and, more particularly, to multi-speed power transmissions having at least six forward speed ranges and incorporating three planetary gearsets.
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive mechanism. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times as the transmission ratios are interchanged. The number of forward speed ratios that are available in a transmission determines the number of ratio interchanges that can occur and therefore the number of times the engine torque range can be repeated.
Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point, during cruising, other than the most efficient point. Therefore, manually shifted (countershaft transmissions) were the most popular.
With the advent of three and four speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improve the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
It has been suggested that the number of forward speed ratios be increased to five and even six speeds. This has been accomplished in many heavy truck powertrains. Six speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992; U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997, U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000; U.S. Pat. No. 6,083,135 issued to Baldwin et al. on Jul. 4, 2000, and European Patent Application No. EP 1 033 510 A1 published Jun. 9, 2000.
Six speed transmissions offer several advantages over four and five speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ six-speed transmissions, such as Polak, passenger cars are still manufactured, for the main part, with three and four speed automatic transmissions, and relatively few five or six speed devices due to the size and complexity of these transmissions. The Polak transmission provides six forward speed ratios with three planetary gearsets, two clutches, and three brakes. The Koivunen and Beim patents utilize six torque transmitting devices including four brakes and two clutches to establish the six forward speed ratios and one reverse ratio. The Lepelletier and the EP publications each employ three planetary gearsets, three clutches and two brakes to provide six forward speed ratios and one reverse ratio. One of the planetary gearsets in each of these publications is positioned and operated to establish two fixed speed input members for the remaining two planetary gearsets.
It is an object of this invention to provide an improved multi-speed power transmission having at least six forward speed ratios and one reverse speed ratio.
In one aspect of the present invention, each of the multi-speed transmissions incorporates three continuously interconnected planetary gearsets and each of the gearsets having three planetary gear members; namely, a sun gear member, a ring gear member, and a planet carrier assembly member.
In another aspect of the present invention, a first member of the first gearset is continuously interconnected with a first member of the second gearset, and a second member of the second gearset is continuously interconnected with a first member of the third gearset.
In still another aspect of the present invention, each of the multi-speed transmissions has at least one gear member continuously interconnected with an input shaft and another gear member continuously interconnected with a transmission output shaft.
In yet another aspect of the present invention, each of the multi-speed transmission mechanisms has five torque-transmitting mechanisms, which consist of either three rotating type torque-transmitting mechanisms, and two stationary type torque-transmitting mechanisms, or four rotating type torque-transmitting mechanisms and one stationary type torque-transmitting mechanism.
In a further aspect of the present invention, the torque-transmitting mechanisms are engaged in combinations of three to provide the six forward speed ratios and one reverse speed ratio.
The present invention defines low-content six speed transmission mechanisms having three planetary gearsets and five selectively engageable torque-transmitting mechanisms. Each of the three planetary gearsets has three members in which a first member of the first planetary gearset is continuously interconnected with a first member of the second planetary gearset, and a second member of the second planetary gearset is continuously interconnected with a first member of the third planetary gearset. The input shaft and the output shaft of the transmission are continuously connected with members of the planetary gearsets.
The first of the torque-transmitting mechanisms connects a member of the first or second planetary gearset with a member of the third planetary gearset. A second of the torque-transmitting mechanisms connects a member of the second or third planetary gearset with another member of the first, second, or third planetary gearset. A third of the torque-transmitting mechanisms selectively interconnects a member of the first or third planetary gearset or one of the interconnecting members with another member of one of the planetary gearsets. A fourth of the selectively engageable torque-transmitting mechanisms selectively interconnects a member of one of the planetary gearsets with a stationary member, such as a transmission housing. A fifth of the torque-transmitting mechanisms selectively interconnects a member of one of the planetary gearsets with another member of one of the planetary gearsets or with the stationary member of the transmission.
By selectively engaging the five torque-transmitting mechanisms in combinations of three, it is possible to provide at least six forward speed ratios and one reverse speed ratio between the input shaft and the output shaft of the transmission.